1. Field of the Invention
The present invention relates to fire suppression systems, and more particularly, to fire suppression systems for substantially airtight enclosed spaces.
2. Background Information
Enclosed area fire suppression methods such as those commonly used in aircraft may also be used elsewhere. Critical features of these fire suppression systems are reliability and self-sufficiency. However, in aircraft and similar settings, efforts to minimize bulk are also essential. This leads to long term efficiencies, including fuel savings in aircrafts (or other modes of transportation) and more work space or storage space when used in other environments. Sometimes the bulkiest component in a fire suppression system is the chemical or compound (i.e., extinguishant) used to extinguish the fire. As an example, this may be 300-400 pounds of Halon (CBrF.sub.3) extinguishant in an aircraft system. Hence a difficult trade-off must sometimes be made between having an adequate fire suppression system and one that is not bulky.
A problem typically arises in connection with fires because the particular location of the fire is unpredictable. Thus, enclosed area methods of fire suppression conventionally provide a minimum concentration of extinguishment within the enclosed area. The methods which do this essentially involve thoroughly mixing an extinguishant and air in the compartment.
Instead of selecting water as the extinguishant, enclosed area fire suppression methods (for example, in aircraft) typically employ bromotrifluoromethane ("CBrF.sub.3), or a related compound bromochlorodifluoromethane, sold commercially as "Halon". Maintaining a minimum concentration of CBrF.sub.3 in a compartment presents a special problem when the concentration is maintained for prolonged periods. CBrF.sub.3 is most practically stored in its liquid form under pressure. As pressure decreases during, for example, piping into the enclosed area, the CBrF.sub.3 vaporizes. Within a system having conduits, this phase change is transient, and therefore it is difficult to achieve a steady state flow of the CBrF.sub.3. Consequently, during a lengthy dispersion there is substantial waste of CBrF.sub.3.
The state of the art of enclosed area fire suppression methods still concerns mixing extinguishants and air in the compartment. Many methods focus on mixing extinguishants with air in order to take advantage of the heavier-than-air characteristic of extinguishants. CBrF.sub.3 in the gas phase is about five times denser than air. Thus, CBrF.sub.3 descends through air, much as sand falls through water. The quantity of extinguishant which is required by conventional methods is unsatisfactorily large. Some prior fire suppression systems are discussed below.
Miller et al. (U.S. Pat. No. 5,211,246) concern a fire suppression method and system for use in an enclosed area, such as in the interior of an aircraft. Miller et al. disclose dispersing a fire retardant material in a layer across the top of an upper region of the enclosed area, while maintaining a sufficient concentration of the material to suppress any fire with which the layer comes into contact. The layer is permitted to descend from the upper region through the middle and lower regions of the enclosed area until the layer has settled near the floor. The descent of the fire retardant material in Miller et al. scours the entire area to suppress the fire.
Fleming (U.S. Pat. No. 5,183,116) is directed to a fire extinguishing discharge system which discharges a fire extinguishing material at a predetermined mass flow rate to maintain adequate concentration of fire extinguishing material in the space.
Hindrichs et al. (U.S. Pat. No. 5,036,867) relate to a fire protection system for extinguishing fires in the cargo space of an aircraft. The system includes two containers for providing extinguishing evaporating liquid, and a common conduit system with nozzles for distributing the liquid. The Hindrichs et al. system is specifically directed to preventing the fire extinguishing medium within the system from freezing (i.e., turning to a solid form).
Miller (U.S. Pat. No. 4,726,426) relates to a fire extinguishment system for an aircraft passenger cabin, wherein a fire extinguishment chemical is provided through the environmental control system of the aircraft.
Baetke (U.S. Pat. No. 4,646,993) is directed to sidewall vent valves for an aircraft. The sidewall vent valves are located in the deck of the aircraft between the skin of the aircraft fuselage and the sidewall panels to selectively prevent and permit fluid communication between an upper and lower compartment of an aircraft.
Bruensicke (U.S. Pat. No. 4,646,848) concerns a fire suppression system for an aircraft including a plurality of ducts which couple a plurality of sub-compartments of the aircraft. The ducts are arranged to distribute the fire suppression chemical in a specific pattern.
Miller (U.S. Pat. No. 4,643,260) discloses a fire suppression system including a first rapidly discharging Halon container (I) and a second metered discharging Halon container (II). The first container is discharged to insure a minimum enclosed compartment concentration of 5% Halon by volume for an initial flame knockdown. The discharge of the second bottle occurs when the Halon concentration as a result of the discharge of the first container drops to 3%. Miller teaches that the Halon gas is introduced near the ceiling at a controlled rate and the gas is dispersed uniformly throughout the cabin so that the location of the fire need not be known.
Bruensicke (U.S. Pat. No. 4,552,325) relates to an emergency smoke disposal system for pressurized aircraft wherein a normally closed smoke evacuation outlet in the skin of the aircraft is actuated to discharge smoke from the aircraft cabin. The evacuation outlet is oriented in an upper portion of the aircraft such that the smoke which accumulates at the top of the aircraft will escape.
Enk (U.S. Pat. No. 4,351,394) is directed to a fire protection system for use in aircraft including a manifold system for providing a fire extinguishing compound to a selected area.
Uematsu (U.S. Pat. No. 3,753,466) discloses an automatic fire extinguishing device for use in copying machines.
Goodloe et al. (U.S. Pat. No. 3,486,562) disclose an apparatus for detecting and extinguishing a fire in an enclosed environment, including a temperature sensor that is activated when a temperature threshold is reached. When the temperature sensor is activated, the gaseous contents of the enclosed area are evacuated to a second enclosed area (accumulator) which is at a substantially lower pressure than the enclosed environment. Substantially simultaneously, nitrogen is introduced into the enclosed environment from a bottom portion of the compartment to take the place of the gases which have been evacuated from the enclosed environment.
Levy et al. (U.S. Pat. No. 3,465,827) relate to an on-board vehicle fire protection system including an air duct opening into the passenger compartment coupled to a foam generating apparatus for providing foam into the passenger compartment.
None of the above discussed patents disclose, teach or suggest releasing a non-combustible gas (e.g., helium) in a substantially enclosed area which forces the gases (i.e., air) present in the enclosed area in either an upward or downward direction in order to effectively suffocate a fire, wherein a fire extinguishing mixture including a non-combustible gas and a fire extinguishing compound are introduced into the enclosed area, and wherein an actuatable gas purging door is opened which enables the air present in the enclosed space to be evacuated therefrom.